Hannover 2020 – scientific programme

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MO: Fachverband Molekülphysik

MO 9: Femtosecond Spectroscopy I

MO 9.4: Talk

Wednesday, March 11, 2020, 11:45–12:00, f102

Effect of External Electric Field on Vibronic and Excitonic Properties of P3HT Studied by Femtosecond Time-Resolved Spectroscopy and Density Functional Theory — •Debkumar Rana, Patrice Donfack, Vladislav Jovanov, Veit Wagner, and Arnulf Materny — Jacobs University Bremen, Department of Physics and Earth Sciences, Campus Ring 1, 28759 Bremen

Poly(3-hexylthiophene-2,5-diyl) (P3HT) is of interest for solar cell applications. However, important elementary processes under operational conditions, i.e., in the presence of applied electric fields, are not yet completely understood. In our work, we have used density functional theory (DFT) to evaluate the field-effect on the vibronic properties of P3HT within and beyond the range of typical external electric field strengths. We demonstrate that charge-phonon coupling and hence charge localization increase with field strength. In parallel, we have used femtosecond time-resolved spectroscopy to study the excitonic properties of P3HT thin films in a model P3HT device under operational conditions. We show that polaron-pair (PP) dissociation into charge carriers occurs in the P3HT device more significantly with increasing reverse bias, consistent with the electric field-induced dissociation of oppositely charged species. Moreover, besides PPs directly originating from hot excitons, we experimentally observe PP formation during exciton dissociation via a field-mediated generation process resulting in a slower contribution to the overall decay dynamics. Transient-absorption anisotropy measurements elucidate the excitation polarization memory loss due to external electric fields.